1. Field of the Invention
This invention relates to thixotropic polyurethane systems, to their production and to their use.
2. Statement of Related Art
In many applications of polyurethane systems, particularly in the field of adhesives, it is desirable that the systems show pseudoplastic to thixotropic behavior so that, after application, a high viscosity is rapidly established and the coating applied is prevented from running.
The present invention relates in particular to special two-component adhesive systems of the polyurethane type which may be used above all in the manufacture of filters, in the fitting of glass in window profiles, particularly for multiple glazing, and in the production of sandwich elements, for example truck superstructures.
In these applications in particular, it is desirable that the adhesive system should not flow because it often has to be applied to overhead or vertical surfaces. Paste-form, filled adhesives which may additionally contain inorganic and/or organic thickeners have hitherto been used for this purpose. In the case of two-component systems, it is generally the polyol component which filled, more particularly with fillers for physical thixotropicizing, inorganic fillers, such as layer silicates, mostly being used.
Paste-form, physically thixotropicized adhesive systems of this type do not flow and although this may be desirable for actual assembly, it is undesirable so far as application of the adhesive is concerned. On the one hand, it makes application by machine difficult, if not impossible; on the other hand, these adhesives do not run on the surface of the substrate with the result that the wetting required is not obtained unless additional measures are taken. In addition, mixing of the filled polyol component with the isocyanate component immediately before application of the adhesive is complicated to a considerable extent.
The problem addressed by the present invention was to provide two-component thixotropic polyurethane systems which would be particularly suitable for the stated applications and which would not be attended by any of the above-mentioned disadvantages, but instead would still have the relatively low viscosity required for application for a few seconds after mixing of the components and in which the thixotropic consistency would only be established after that time; in addition, the typical requirements of a corresponding adhesive system would be satisfied.
It has surprisingly been found that two-component polyurethane systems of the type in question can be obtained if the polyol component contains a mixture of polyamidomines with a low molecular weight polyfunctional amine. Other advantageous embodiments of the invention, which also relate to the production and use of the thixotropic polyurethane systems according to the invention, are disclosed in claims 2 to 16.